This application is related to U.S. patent application Ser. No. 680,725, filed Dec. 12, 1984, now abandoned.
The present invention generally relates to a hand apparatus of an industrial robot. In particular, it relates to an apparatus for effectively causing a floating mechanism including a simple energizing spring to perform any one of a number of gripping functions of double hands.
FIGS. 1 and 2 are diagrams showing the conventional double hands provided with a floating mechanism. Such hands are disclosed, for example, in Japanese Unexamined Utility Model Publication No. 55-66789, and FIG. 1 is a perspective view of such a hand. FIG. 2 is a side view of FIG. 1. As shown in these drawings, a double hand is composed of a pair of grippers 3 and 4 arranged parallel to each other and displaced along the direction of a central axis, as indicated by a single-dot chain line 2. The two grippers 3 and 4 are used for gripping a workpiece. Respective pairs of gripping pawls 5 and 6, provided on the grippers 3 and 4, are arranged to be openable and closable in respective planes that are perpendicular to the central axis 2. The pawls 5 and 6 are actuated through respective link mechanisms 7 and 8. The opening and closing of the gripping pawls 5 and 6 is performed by actuators (not shown) provided in the respective base portions of the grippers 3 and 4. Four floating elements 9 are each composed of an elastic body such as a spring or the like and are placed between the grippers 3 and 4. A joint 10 allows for the rotation of the double hand 1 and is connected through a wrist mechanism 11 to an arm 12. The upper gripper 3 is directly connected to the joint 10 while the lower gripper 4 is connected to the joint 10 through the resilient floating elements 9.
In the described conventional double hand having the floating mechanism, a workpiece 13, indicated by a double-dotted chain line of FIG. 2, is gripped by the lower pair of gripping pawls 6 of the gripper 4 and is then conveyed in the direction of the arrow to be grasped by a chuck of a lathe. The workpiece 13 as a result presses the lathe chuck, and therefore a reaction force is exerted in the chuck. The reaction force, in turn, is exerted onto the floating elements 9 through the lower gripping pawls 6 and weakened by the floating elements 9 so that the reaction force is softened.
Next, when the gripper 4 and the gripping pawls 6 have been cycled through one set of operations including gripping and conveying, the wrist mechanism 11 is rotated by 180.degree. so as to cause the gripping pawls 5 of the gripper 3 to carry out the next operation, which is similar to that carried out in the preceding cycle with the gripper 4. Therefore, in the second operation, the reaction force generated when the workpiece 13 is forced against the chuck is not exerted on the floating elements 9 because the gripper 3 is directly fixed on the joint 10. Accordingly, the gripper 3 is used only for carrying out such a process where no buffer action is required against the reaction force.
In the thus-arranged conventional double-hand apparatus provided with the floating mechanism, there have been problems, specifically, that the apparatus has a complicated mechanism including a plurality of floating elements. Furthermore, the reaction force exerted on a workpiece is absorbed by the floating mechanism, and a vertical force component of this reaction force is produced which makes it difficult to correctly set the workpiece. Also, among the reaction forces exerted onto the hands in different situations, only the reaction force exerted on the hand provided with the buffer mechanism is absorbed.